<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>promise A+ 规范</title>
</head>
<body>
<script>
let a = `onFulfilled,onRejected 不会立马调用，而是被留存下来，留存到整个promise 进入已决状态，根据状态的区分而进行调用，所以这里不能用一个变量
而是用一个数组 then是可以绑定多次的， `;
const PENDING = 'pending';
const FULFILLED = 'fulfilled';
const REJECTED = 'rejected';
class myPromise {
constructor(executor) {
this.status = PENDING;
this.data = null;
this.reason = null;
this.dispatchers = [];
try {
executor(this.__resolve.bind(this), this.__reject.bind(this));
} catch (err) {
this.__reject(err);
}
}
__resolve(data) {
this.__updateStatus(FULFILLED);
this.data = data;
this.__executeDispatchers();
}
__reject(reason) {
this.__updateStatus(REJECTED);
this.reason = reason;
this.__executeDispatchers();
}
then(onFulfilled, onRejected) {
return new myPromise((resolve, reject) => {
this.dispatchers.push(
{
status: FULFILLED,
dispatcher: onFulfilled,
resolve,
reject
},
{
status: REJECTED,
dispatcher: onRejected,
resolve,
reject
}
);
});
}
catch(onRejected) {
this.then(null, onRejected);
}
__updateStatus(newStatus) {
if (this.status !== PENDING) return;
this.status = newStatus;
}
__executeDispatchers() {
if (this.status === PENDING) return;
for (const dispatcherConf of this.dispatchers) {
this.__executeDispatcher(dispatcherConf);
}
}
__executeDispatcher({ status, dispatcher, resolve, reject }) {
if (this.status !== status) return;
if (typeof dispatcher !== 'function') {
this.status === FULFILLED ? resolve(this.data) : reject(this.data);
}
try {
const result = dispatcher(this.status === FULFILLED ? this.data : this.reason);
resolve(result);
} catch (err) {
reject(err);
}
}
}
const myPro = new myPromise((resolve, reject) => {
setTimeout(() => {
resolve(11);
}, 1000);
});
myPro.then(r => {
console.log(r);
});
</script>
</body>
</html>
